Factors affecting Merino wool contamination in crossbreeding

Abstract

Fleeces of Merino ewes were tested to identify whether contaminant sheep fibres increased from Damara-ram mating alone, whether extent of colouration of the crossbred lamb coat, day of birth and number of lambs being reared affect transfer to the maternal fleece, and whether increased fleece bulk or shearing the ewes 3.5 months post-weaning reduced the concentration of contaminant fibres. Measurement of fleeces from 26 ewes mated to a Merino ram and 26 ewes mated to a Damara ram did not show a significant increase in the presence of pigmented or heavily medullated white fibres. In contrast, wool samples from 54 Merino ewes taken the day after weaning of their Damara crossbred lambs showed pronounced contamination by pigmented fibre as well as relatively high levels of heavily medullated white fibres. The concentrations of pigmented fibres were highest in the fleeces with short wool and proportionally diluted in the fleeces with long wool. Concentrations of heavily medullated white fibres from white-spotted coats of the crossbred lambs showed that ewes that reared multiple lambs had greater transfer while the day of birth after the start of lambing and the extent of coat colour on the lambs were both negatively related to transfer of these fibres. Side samples collected from the same 26 ewes at weaning and 3.5 months after weaning revealed declines in contaminant fibres greater than could be explained by dilution by new wool growth after weaning, implying physical loss from the fleece. However, the residual contaminant fibres after 3.5 months' delay in shearing remained excessive for Merino wool. Wool samples from the sheep's side produced similar concentrations of contaminant fibres as the fleece grid sample.